Swamp Things

Florida’s uninvited predators.

The state’s ecology is a kind of urban legend come true—the old alligator-flushed-down-the-toilet story, with a thousand species.Credit CHARLES BURNS

Just before daybreak, in the eerie hour after Hurricane Andrew struck southern Florida, a zoo worker named Ron Magill went to see what was left of his animals. He’d spent the night in his ranch house in suburban Miami, huddled in the master bedroom with his wife, who was nine months pregnant with their first child. They’d propped a mattress and an armoire against the sliding glass door, but could still feel it flexing beneath the bellowing wind. When the shutters flew off the windows, the pressure fell so suddenly that Magill’s ears popped, as if he’d fallen from a great height. “I remember going outside afterward, and it was like ‘The Wizard of Oz’ in reverse,” he says. “I went from the color of my living room to the black-and-white of devastation.”

Across the street, a van had been flipped upside down and flung against a house; here and there trees were stuck in rooftops like toothpicks in canapés. Andrew was a Category 5 hurricane, small but tightly focussed, with winds of up to a hundred and seventy-five miles an hour. It made landfall near the city of Homestead on August 24, 1992, and cut a swath through some of the state’s most populous areas. When it was over, twenty-five thousand homes had been destroyed and fifteen thousand boats lost, sixty-five people were dead and a hundred thousand permanently displaced. It was the costliest natural disaster in American history up to that time.

It was also a brief window on the ecology to come. As Magill was driving to the Miami Metrozoo, where he is the communications director, he passed a troop of rhesus macaques scampering up the road, as if on the plains of Kashmir. Later, the monkeys were spotted wandering through nearby farm fields, gorging themselves on tomatoes. Elsewhere, a small antelope was found wandering the halls of an administration building, a group of juvenile baboons broke into the weight room of a private home, and a python was found dead on the beach in Miami, with two full-grown raccoons in its belly. It was as if all Florida had turned, for a moment, into Disney’s Animal Kingdom.

When Magill arrived at the zoo, it was in ruins. The monorail had been wrenched from its steel stanchions, its tracks twisted like a coat hanger. A six-horse trailer had been tossed over a ten-foot fence and into the rhino enclosure, and a new five-million-dollar aviary had blown away. “It was like God had come through with a twenty-five-mile-wide weed whacker and just levelled the place,” he says. Miraculously, though, almost all the animals had survived: the zookeepers had herded them into a few bunkerlike buildings. The escapees that Magill had seen were mostly from private collections.

Florida is an “Ellis Island for exotic animals,” Magill says. Some twelve thousand shipments of wildlife enter the country at the Port of Miami every year, second in number only to Los Angeles, and the state is home to thousands of pet stores, breeders, and animal-research facilities. “We’re a biological cesspool of introduced life,” another biologist told me. The Florida Fish and Wildlife Conservation Commission estimates that between three and four thousand primates escaped during the hurricane, together with as many as fifteen thousand other animals, including parrots, gazelles, wallabies, six mountain lions, and an Asian pheasant caught loping down the Florida Turnpike. The majority were rounded up or exterminated. (A rumor soon spread that the roving macaques, which were from a primate-research center, had been infected with AIDS. “It wasn’t true,” Magill says. “But pretty soon people were in the streets shooting them with shotguns. It was completely surreal.”) What happened to the rest isn’t clear.

Only a few months earlier, for instance, a new warehouse for exotic reptiles had opened in Homestead. The owners couldn’t afford to build a stormproof facility, so they’d rented an old greenhouse instead. “It was really makeshift,” Patrick Reynolds, a lieutenant with Florida Fish and Wildlife, told me. “Everything was in Dixie cups and plastic dishes—stacks and stacks of them. The little ones were for frogs and scorpions and tarantulas. The larger ones were for snakes.” Reynolds remembers seeing hundreds of Burmese pythons among the stock. They were just babies then, a few inches long, but would grow into some of the world’s largest and deadliest reptiles. “And, well, Hurricane Andrew came through and the wind just took them, and—whoooooo!—off they went. There wasn’t one stick of that greenhouse left.”

Curled up in their flat plastic containers, those animals could have flown for miles—Frisbees, flung by the storm. Or so Reynolds and other wildlife managers speculate. Most of the animals would have died in flight, victims of what Reynolds calls “the blender effect.” But a few may have survived long enough for a landing, in some saw-grass marsh or a cypress slough, and slithered off in search of food or a mate. The wind was blowing west that day, straight for the Everglades.

To a Burmese python, Florida offers more than freedom from a cage, more than a warm spot on a chilly continent. It offers virgin hunting grounds. The peninsula last began to emerge from the sea around a hundred and twenty-five thousand years ago, when the waters of the Caribbean, drained by glaciers to the north, gradually drew back to reveal a vast seabed, table flat beneath its scruff of vegetation. Much of the state is barely above sea level—one reason it’s so vulnerable to hurricanes—and shrinking steadily. At the height of the last ice age, it was more than twice its current size. As one biologist put it, “Florida was underwater not too long ago and it will be again soon. Global warming is gonna fix this problem.”

The peninsula is almost an island, in ecological terms: water on three sides, frost on the fourth. Its isolation has preserved an odd menagerie of prehistoric creatures—alligators and crocodiles, sawfish and sea turtles—but discouraged many immigrants. With no tropical neighbors to lend it species, Florida has been colonized mostly by northerners: red-tailed hawks, white-tailed deer, raccoons, and opossums. They’ve been joined by an abundance of birds and a handful of tropical castaways: frogs and snails rafted over from the Caribbean and South America, spiders ballooned in on storms. And yet, compared with most areas of similar warmth and fecundity, southern Florida has few native species. “Look at our lizards,” Scott Hardin, the exotic-species coördinator for Florida Fish and Wildlife, told me. “We have sixteen. Cuba alone has eighty-three.” To those lucky enough to find it, in other words, the state is less Ellis Island than Club Med: an exclusive seaside getaway, far from the fang and claw of the usual tropical crowd.

The Everglades have existed for only about five thousand years, and for most of that time they’ve been left to themselves. When people first arrived, near the end of the last ice age, Florida was a windswept savanna roamed by mammoths, sabre-toothed cats, and giant armadillos. As the climate turned wet and warm, the great beasts died off—what the heat didn’t kill, the hunters did—and the prairie slowly rotted to marsh. It was a landscape unlike any other on the continent, a “soggy confusion” of land and water, as Michael Grunwald writes in his epic history, “The Swamp.” Though it lacked the dizzying diversity of the Amazon, no other place had its mixture of tropical and temperate species—southern crocodiles next to northern alligators—and a few so odd they seemed to come from another planet: ghost orchids, pig frogs, strangler figs, and carnivorous plants.

The Spanish, beginning in 1513, planted their flag on the coast along with a few of their favorite crops: citrus trees and sugarcane, wheat and barley. But the Everglades still belonged to the natives. When Ponce de León tried to prove otherwise, they shot him with a poison arrow. The marsh was too wet for farming, too unpleasant for settling. One naturalist accused it of furnishing “as much laceration and as many annoyances to the square inch as any place I have ever seen.” Another, Grunwald notes, caught a third of a million mosquitoes in a single trap in a single night. By 1897, when an explorer named Hugh Willoughby crossed the Everglades in a dugout canoe, most of North America had long since been tamed, but southern Florida, in Willoughby’s words, was “as much unknown to the white man as the heart of Africa.”

The colonists eventually carried the day, of course—with some help from the Corps of Engineers. Marshes were drained, canals dredged, bedrock ground into a mean soil. But it was only in the nineteen-sixties, after plants like hydrilla and water hyacinth, imported as ornamentals, had clogged up canals and irritated pleasure boaters, that people began to notice how thoroughly the landscape had changed. Where stands of coco plum and mahogany once stood, there were now thickets of Brazilian pepper, a relative of poison ivy. Where meadows of purple muhly grass grew, there were forests of Australian melaleuca, their blossoms as blandly scented as fresh-cut potatoes. After five centuries of turning pine groves to orange groves, Floridians had settled on an image of how nature should look. And these plants didn’t belong.

The invasion, though, had just begun. Over the next fifty years, Florida’s plant nurseries were joined by a thriving exotic-wildlife trade, sending a ragged parade of escapees into the wild: parakeets, peafowl, swamp eels, and giant ratlike capybaras. Troops of runaway squirrel monkeys were swinging from trees in Fort Lauderdale long before Hurricane Andrew, and spiny-tailed iguanas were lounging on branches in Boca Grande. Pet stores made a habit of bringing in new exotics every year. Iguanas were in fashion for a while, then marmosets and poison-arrow frogs. “In the eighties, everyone wanted furry animals,” Patrick Reynolds recalls. “Cougars and lions and tigers. Those were the cocaine-cowboy days. Then, in the early nineties, the reptile explosion started.”

Florida now has more exotic lizard species than there are natives in the entire Southeast. On a single tree you could conceivably find plants and animals from six continents, including parrots from South America, mynah birds and Old World climbing ferns from Asia, vervet monkeys from Africa, ladybird beetles from Australia, and feral cats from Europe, via Africa and Asia. In some cases, the recent immigrants would be more genetically diverse than their cousins back home. The state’s ecology is a kind of urban legend come true—the old alligator-flushed-down-the-toilet story repeated a thousand times with a thousand species.

Some find all this thrilling: Florida has become an open-air zoo, richer in species than ever before. To others, it’s the harbinger of a new and depressingly undifferentiated age, when the old biological borders begin to fade and every place starts to look like every other. Ecologists have even given it a name: the Homogecene.

When Burmese pythons began to appear in the Everglades, in 1995, the state wildlife authorities didn’t give them much thought. Snakes like these had turned up before. Burmese pythons were among the most popular exotics in pet stores at the time. They were cheap—twenty to thirty dollars a snake—easy to feed, and less temperamental than boas. The hatchlings looked harmless lying on a heat rock in a terrarium, and the store owners were happy not to correct that impression. “I remember thinking, Is everybody buying these things?” Reynolds says. “Well, apparently so. The craze was on. We were pulling twenty-foot pythons out from under little houses in Coconut Grove. Nobody cared. They didn’t have a chance to breed that we knew about.”

The escapees were usually caught in the suburbs or near the edges of the park, and were almost always full grown. Invariably, they’d come from a pet shop or a breeder, or been set free by an owner who found himself with more snake than he could handle. As Skip Snow, a wildlife biologist at Everglades National Park and its chief python hunter, later put it in a PowerPoint presentation, “Do you really want a snake that may grow more than twenty feet long, weigh two hundred pounds, urinate and defecate like a horse, live more than twenty-five years, and for whom you will have to provide mice, rats, and eventually rabbits?”

Still, the pythons found in the mid-nineties didn’t fit the usual pattern. They ranged in size from juveniles to adults, and they were all caught deep in the park, in the saline glades to the southeast. Why would anyone drive that far just to dump some snakes?

Snow isn’t sure how the pythons got to the Everglades. But he, for one, doesn’t buy the Frisbee theory. Assuming the snakes survived the hurricane’s blender effect, why didn’t a few of them land closer to the reptile warehouse in Homestead? The mystery deepened when no more snakes were found for a while. Another pair showed up in 2000, and three more the following year. But there never seemed to be enough to prompt an official response. Snow was a “backcountry specialist” at the time, marking trails and scouting the wilder reaches of the park. He was concerned about the pythons, he says, but he had a hard time interesting others in them. “People kept saying, ‘You haven’t found a nest. You haven’t seen very many.’ There was a lot of denial, in my opinion.” Burmese pythons had rarely been studied in their native habitat, and it wasn’t clear that they could survive in the Everglades. “So people just made stuff up,” Snow says. “ ‘The cold weather will kill them.’ ‘Fire ants will eat their eggs.’ If they could find an excuse, they’d make an excuse.”

The situation wasn’t unique to the Everglades. After more than half a century of studying invasive species, biologists still can’t tell which ones will die off and which ones will run rampant. Some, like the English house sparrows imported to New York City in the eighteen-fifties, start multiplying soon after they arrive. Others lie low for decades. “Reptiles have a tremendous amount of patience,” Snow says. “They can wait out harsh environmental conditions. They can go without eating for a long time. Then, all of a sudden, there’s a phase shift, a trigger point. The population starts to function as a population rather than as a lone inoculation.” In a place as remote as the Everglades, he adds, that moment is almost impossible to predict. “When do you draw the line? When do you take action to avoid that logarithmic point where things take off exponentially?”

The decision, in the end, was made for him. One January morning in 2003, a group of tourists were walking along the Anhinga Trail, not far from the park’s main entrance, when they noticed something splashing in the shallows nearby. When they went to take a closer look, they were witness to a death match. A full-grown alligator had clamped its teeth on an adult python and was ensnared in the snake’s coils. The fight went on for more than twenty-four hours, with the alligator, by all accounts, getting the better of it. By the time it loosed its jaws and the mangled snake slithered away, thousands of pictures and hours of videotape had been taken, and accounts later appeared in outlets as disparate as the National Examiner (“GATOR VS. PYTHON!”) and National Geographic. “The park superintendent called me after that,” Snow recalls. “He said, ‘We’ve got a problem.’ ”

Within months, Snow was finding pythons of all sizes in the park, including hatchlings—proof, if any more were needed, that the snakes were breeding. That summer, he took one of the hatchlings to a meeting of the state’s wildlife managers. “Here it is 2003, and we’ve spent all these years waiting for the standard of guilt to be met,” he says. “So I show up with this little python and pass it around.” The others took one look at it, he says, and told him that he was out of luck—Burmese pythons were in Florida for good. “In one week, we’d gone from ‘No problem at all’ to ‘You might as well give up.’ ”

Snow, who is fifty-seven, has the dour, keen-eyed look of a large waterbird—natural enemy of snakes. His face is thin and angular, its balding dome crowned by gray bristles. He has long legs, sloping shoulders, and a craning neck. When folded up behind the wheel of a car, as he often is, on his python-hunting trips, he can never seem to get comfortable, bobbling up and down and bending at the waist, squinching his eyes and jerking his head to the side. Yet he keeps his truck at a maddeningly slow pace, eyes fixed on the shoulders of the road.

“I won’t pass up a snake,” he told me as we were driving through the park one afternoon. “I may not be looking with every ounce of my body every minute. But there are search images that get developed: the feel, the look, the body posture, and head shape—all these things together.” The day before, as we were leaving the park, Snow had suddenly swerved his truck around and doubled back down the road. He’d seen a black shape winding across the asphalt, he explained, but by the time he stepped out to catch it, it was gone. “Probably just a water moccasin,” he said—poisonous, but only a fraction of a python’s size.

Snow has spent his entire career with the park service. After earning a master’s degree in environmental sciences from Miami University in Ohio, he took positions at Mt. Rainier and at Theodore Roosevelt National Park, in North Dakota. The Dakotas were pristine and starkly beautiful: canyons of striated sandstone, patrolled by golden eagles and pronghorn antelope. In the spring, lightning would sometimes ignite the coal deposits underground, firing the clay above them into brick-red porcelainite. Snow and his wife, whom he’d met while still in high school in Cleveland, spent eight winters in the park and had a boy and a girl. But the cold and isolation could be hard to bear. The closest big city was Bismarck, three hours away; the closest thing to a social life shooting hoops with the two other park-service employees in the district. In 1988, Snow applied for a post in the Everglades, hoping to find a warmer, more stimulating habitat for his family. Chasing giant snakes wasn’t really what he had in mind.

He lives in Miami now and commutes to the Daniel Beard Center, in Everglades National Park. The research center sits in what’s known as the Hole-in-the-Donut, an area at the heart of the park that was long ago cleared for farming and the military. From Snow’s office, in what was once an Army barracks, he can see a pair of low bunkers built to house Nike missiles after the Cuban missile crisis. But the Burmese python has come to seem a far more immediate threat. Snow and his colleagues have found more than nine hundred so far—three hundred and eleven in the past year alone. At best, he estimates, they represent ten to fifteen per cent of the total population; at worst, fewer than one per cent. The Everglades, at full capacity, could hold as many as a hundred and forty thousand pythons.

“There was that movie ‘Gremlins,’ ” he said as we were driving. “They had these cute little things that, if they got out, they got out of control. Well, some wildlife is like that. These things get huge.”

In the summer, pythons come out at night to hunt. In the winter, they emerge during the day, to bask in the brief sun. It was December now. The light was fading early, and the marsh was already alive with creaking and buzzing, flapping and cawing. On either side of the road, stands of slash pine sent shadows across the road, spindly as flamingo legs. In the distance, a string of low, bushy islands hung between marsh and sky—faint pulses on the horizon’s flat line. The Everglades are a river of grass more than fifty miles wide and a hundred miles long—a landscape so innocent of topography that its mountains are measured in inches and even the largest predators try to keep a low profile. Burmese pythons are semi-aquatic: they’re happy to hunt or swim in salt water or sweet, but they have to sleep and lay their eggs on dry ground. In the Everglades, they prowl from island to island, nesting in sandy soil or crawling onto patches of cattails. “They don’t need much—any little island will do,” Snow said. A snake may stay there for a few days, brooding or digesting in some comfortable hole, well sheltered from the wind, then head into the marsh again for another meal.

Snow has learned these habits largely through radio tracking. In the past three years, he has implanted twenty-five pythons with Tootsie Roll-shaped transmitters and tracked their movements across the marsh. His equipment can be accurate to within a couple of inches, and he has followed the snakes by airboat, motorboat, helicopter, canoe, truck, and on foot. Yet they still slip from his grasp. More than once, he has stood knee-deep in the muck, a beeping radio tracker in hand, convinced that a snake is at his feet. But he can’t see it. Its movements are too silky, its olive-brown skin too well steeped in the murky water. “You know that the snake is right there,” he said. “It makes no sound, doesn’t rustle. Then all of a sudden it’s over there.”

To go any great distance, an animal usually has to cross a road. When it crosses a road, it runs the risk of getting spotted or squished. (Some biologists call this the “rapid-acceleration removal method.”) Snow’s best strategy, therefore, is to wait for the snakes to come to him. An enterprising python may travel more than a mile in a day, his tracking has shown, so sightings are not uncommon. Earlier that day, he had found a dead juvenile along the main park road, its skin ground into the gravel and shredded by a tire. The week before, he and another park employee had caught a live fourteen-footer. They’d grabbed it by its tail and yanked it onto the asphalt, pinned its head with a snake stick—a metal pole with a retractable noose at its tip—and wrestled it into an ice chest, for later dissection.

Pythons aren’t venomous, but their upper jaws are fitted with a quadruple row of sharp, inward-curving teeth, their lower jaws with a double row. They use the teeth to gain purchase on their prey until they can coil their body around it. Snow’s advice is simple: “Stay away from the pointy end.” Even a small snake can cause a sizable wound and squeeze your arm hard enough to cut off the blood flow. The large ones have been known to swallow leopards whole. “It’s just an absolutely absurd animal to have to deal with,” he said. “The fact that they’re even here. The fact that we even have to have this conversation. It’s just off-the-charts crazy.”

Scientists who study invasive species tend not to talk like scientists. They talk like detectives on a homicide squad, or generals in a Japanese monster movie. They count deaths, predict extinctions, warn of alien takeovers. They’re used to being ignored.

Since 1900, the federal government has kept lists of injurious species that are forbidden from entering the country. They include disease carriers like Indian wild dogs and flying foxes, well-known invasives such as zebra mussels and brown tree snakes, and noxious weeds such as devil’s thorn, goat’s-rue, and giant hogweed. But adding a species to the list can take as long as a decade—the Fish and Wildlife Service has a single person assigned to the task—and enforcement is a constant struggle.

Every year, more than a third of a billion exotic plants enter the Port of Miami, along with its twelve thousand shipments of exotic wildlife. The United States Fish and Wildlife Service can afford to inspect only one in ten to twenty shipments—the ones that seem most suspect. “Even if we think we’re catching a lot of people, it’s probably only twenty-five per cent,” Eddie McKissick, the service’s lead agent at the port, told me. “It’s like anything else—you catch them, they change their ways.” Profits from international wildlife smuggling, the Department of Justice has estimated, are second only to those from drug smuggling.

McKissick is fifty-one and still enjoys the chase. He drives a black Crown Victoria Interceptor (“This sucker will scat!”), keeps his hair close-cropped and his mustache trim, and reads game-warden memoirs in his spare time: “A Sword for Mother Nature,” “The Thin Green Line.” When his cell phone rings, it sounds like a cavalry charge: Baba ba baba baaaa!

After sixteen years at the port, McKissick has seen or heard of every sort of smuggler’s trick: boxes with false bottoms, bags with hidden compartments, boots made from endangered species and re-covered in common leather. One man was caught with a boa constrictor wrapped around his belly; another had a pair of pygmy marmosets in his fanny pack; yet another tried to sneak in some live finches—he’d crammed the birds into pill bottles and strapped them around his legs. The bond room below McKissick’s office is piled to the ceiling with confiscated corpses: stuffed cobras, dried sea horses, monkey skulls, a rhinoceros head. But live exotics still fetch the best price. A few years ago, inspectors caught a smuggler with a suitcase full of giant bird-eating tarantulas and other exotics from Venezuela. The man had bought the lot for three hundred and fifty dollars, but he could have sold them in the United States for forty-five thousand.

By now, so many exotics have made it to Florida and borne young that local breeders may soon export as many animals as are brought in. When McKissick and I arrived at the port one Monday morning, a shipment of reptiles was headed for South Korea. They were packed in Styrofoam boxes and piled on a pallet in an Air Canada loading bay. McKissick watched as two of his staff, wearing gloves and safety glasses, sliced open the boxes with a razor. When the lids came off, hundreds of hatchlings blinked up at the light. They were crouched in round containers perforated with breathing holes, stacked on top of one another in a reptilian high-rise: snapping turtles with fierce little eyes, flying geckos with suction-cup feet, black-throated monitors flexing their slender, articulate claws. One two-litre soda bottle was filled with bright-green tree frogs, careening off the sides like popcorn at a movie theatre. It was an ecosystem in miniature.

Compared with most, this was a model shipment. “The crates that come in from the Third World—you can literally tear them apart with your hands,” one of the inspectors told me. Many of the animals die in transit, she added, and some of the rest get free in the boxes and are desperate for release. The week before, a shipment had come in from Asia with more than seven hundred animals, including taipans, death adders, and eight other species of venomous snakes. Taipans are among the world’s deadliest reptiles—their bite can be fifty times more toxic than a rattlesnake’s—yet they’ve never made it onto the government’s injurious list. With the right permit, an importer in Florida can sell as many as he likes. None are known to have escaped into the wild so far, but there have been numerous reports of cobras on the loose, as well as anacondas.

McKissick admits to being fond of some exotics—he likes to throw a little fruit to the green iguanas that hang out in his back yard. As for troublemakers like the python, he said, there’s no good way to keep them out of the country. The best you can do is try to exterminate them when they escape. It was an odd admission for someone in his position, but I’d heard similar sentiments from a number of biologists. “It’s time to stop studying these things,” one of them told me, “and time to start killing them.”

Late one afternoon, in a large enclosure behind the research center in the Everglades, Skip Snow and I watched a python go hunting. The snake had been caught a few weeks earlier, on the Tamiami Trail, to the northeast, and implanted with a radio transmitter—the first of three snakes that Snow hoped to track and study more closely in the enclosure. She was a magnificent animal: thirteen feet long and more than seventy pounds. As she moved across the open ground, her body morphed and flowed like melted wax, pooling into thick coils, then thinning into a narrow strand, sinking into the dun-colored grass, then suddenly floating above it, tasting the air with her flickering tongue.

Pythons are carnivorous, but they aren’t picky. Snow and others have found mice, rats, rabbits, muskrats, raccoons, squirrels, bobcats, opossums, otters, deer, ducks, coots, grebes, egrets, and a house cat named Frances in the stomachs of snakes. “I don’t think there is anything they can’t eat or attempt to eat,” he told me. The smaller prey go down in one gulp; the larger ones get a bite and a patient squeeze. But some meals are more obliging than others. Pythons often have teeth torn loose during a struggle and end up ingesting them, and they have trouble swallowing pointy objects: porcupines, for instance, or racks of antlers. One python in the Everglades was found with a great blue heron stuck in its throat. The bird’s bill had poked its way through the back of the snake’s head, and was widening the hole every time the snake tried to swallow it. When the python was on the verge of getting caught, it disgorged the bird and slithered off—presumably to hunt another day.

“You never bet against a snake,” Snow said. “But they do make mistakes.” Four years ago, a thirteen-foot python managed to swallow a six-foot alligator. By the time Snow found them, after a helicopter pilot had spotted them at Shark River Slough in the eastern Everglades, the snake was suffering from extreme indigestion. Its belly had burst open and the alligator’s hind legs were protruding out of it like a pair of vestigial limbs. Some biologists speculated that the victim woke up inside the snake and tried to kick itself free, or clawed through in its death throes. Snow thought the python’s appetite was just too large for its stomach. “That snake made a mistake,” he said.

The question of diet had been much on Snow’s mind lately. He and his colleagues had caught pythons on bridges and on boardwalks, along roadways and along the edges of canals. They’d found one snake inside a tourist’s Ford Explorer, so tightly coiled inside a wheel well that they tried to shock it loose with a Taser. (“This tactic proved unsuccessful,” the park ranger’s report later noted, “as the python began to contract and excrete body fluids all over the four responders.”) But they’d caught only a handful of pythons in the swamp, and they’d never managed to trap one. To lure a snake, he says, you have to have something it really wants. How can you catch an animal that eats everything?

Snow’s latest answer lay along the fence, not far from the python we were watching. It was a rectangular wire trap, with openings at either end. It was positioned to intercept snakes that were following the fence line. To enter it, they would have to crawl down a funnel-like passage and squeeze past a hinged flap. But Snow had doubts about the design. The pythons in the park had shown no interest in it so far—the traps we’d checked earlier that day, near an abandoned lodge in the marsh, were all empty. Why bother crawling through a trap when you could just go around it?

Various state and federal agencies were working on more promising alternatives: traps baited with snake pheromones, thermal cameras that could track a python’s body heat, “Judas snakes” radio-tagged to lead hunters to nests. A beagle named Python Pete had even been trained to track snake skins around the research center, with mixed results. (“He still needs to go to finishing school,” Snow said.) But the new schemes all required more research and funding, and invasive animals are still a low priority in Florida. The state budget for controlling invasive plants, which threaten Florida’s boating and farming industries, is nearly forty million dollars a year. The budget for invasive animals is less than a million.

Inside the preserve, the python had reached the trap and was nudging it with her nose. Instead of crawling inside, though, she slid over to the fence. She found the gap between it and the outside of the trap, wriggled her head into it, and pulsed her body forward, like a drawstring slipping through a hem. Then she lay there, comfortably cradled, and basked in the day’s last light, as if she had all the time in the world.

Burmese pythons have been found as far north as Jacksonville and as far west as Tallahassee. Those snakes were no doubt escapees, but it’s clear that the wild python population is spreading. The only question is how far. Animals pay no regard to political borders, biologists like to point out, and Burmese pythons are better travelled than most. Their native range stretches from the foothills of the Himalayas to the jungles of Indonesia, with everything from prairies to pine forests in between. And although they’re cold-blooded, they’re expert at regulating their body temperature. In the summer, they can climb a shady tree or cool off in a lake (their tails are prehensile, their lungs strong enough to sustain them underwater for half an hour or longer). In the winter, they can coil up in a riverbank or a hollow tree and brumate—the reptilian version of hibernating.

Two years ago, Gordon Rodda, a zoologist with the U.S. Geological Survey, decided to map the python’s potential range in the United States. Together with two colleagues, he gathered temperature and rainfall data from weather stations throughout the python’s native range, then compared them with similar data from the United States. The results were unsettling. “We had the same feeling that other people have, that this is a tropical animal,” Rodda told me. “But once we actually looked at the weather records we were like, ‘Huh. They aren’t as tropical as we thought.’ ” Roughly a third of the contiguous United States lies within the python’s range, they concluded, including all the Southern states and large portions of Texas, Oklahoma, New Mexico, Arizona, and California. By 2100, at the current rate of global warming, the pythons could reach New York City.

Rodda’s scenario is in some dispute. Last August, a team of biologists from the City University of New York, using a different habitat model, predicted that the snakes would stay safely contained in southern Florida. Still, Snow expects the worst. “I see no reason why all of Florida can’t be occupied,” he told me one morning as he was getting ready to dissect a python in his lab. “And they should be able to make a go of it in the southern tier of the U.S.” Pythons can travel long distances, he said, and cross large bodies of open water. “They’re very good swimmers. It’s nothing to think of an animal going five or six miles or more.” A python that finds itself in an unpleasant spot can always slither on.

The snake that Snow was dissecting had been caught in Summerland Key, one of the southernmost of the Florida Keys. To get there, it could have crawled down Highway 1, crossing several bridges along the way, or swum from key to key. Or it might have escaped or been set free by a local resident. The islands were a bad place for pythons to be. They were home to a number of endangered species well suited to the snake’s appetites: Key Largo cotton mice, Lower Keys marsh rabbits, and others. (Florida as a whole has thirty-one threatened or endangered species that are vulnerable to pythons, and another forty-one that are listed as rare.) Several snakes have been caught on the islands with wild animals in their bellies, and python hatchlings have been found on the mainland, just north of Key Largo.

Snow unspooled the snake onto the floor and measured it: eleven feet two inches. Then he lifted it onto the counter, stuck a scalpel in it, and unzipped it like a ski bag. “If the smell starts to bother you, we can open the back door,” he said. “I’m kind of numb to it.” He checked the body for giant-toad ticks—another exotic species, carried in on cane toads from the Caribbean—and peeled back its tapestry skin. As he worked, he hummed a tune under his breath: “I’ve Grown Accustomed to Her Face.”

In the fall, pythons usually fatten themselves up for the winter, Snow said, but this snake had been badly injured, probably by a car. Its tail was lacerated, some of its ribs were broken, and it weighed only twenty-two pounds. He pointed to its pale-pink flesh, its moss-green gallbladder. “I’m seeing virtually no abdominal fat,” he said. “This thing was running on empty.”

You can learn a lot about an animal from its gut—that Burmese pythons don’t much care for fish, for instance. But Snow’s purpose, in this case, was mostly political. If he could prove that the pythons were eating endangered species, it would be much easier to lobby for funds. So far, he’d pulled a few Key Largo wood rats out of snakes, but he could use more charismatic victims. “Not all wildlife is created equal,” he said, extracting a brown wad of what looked like rodent fur from the snake’s intestine. “We did get a wood stork once. And a Florida panther would be right up there—almost as good as a human. But nothing would be as good as the lap dog of a county commissioner.”

The biologists I spoke to seemed a little surprised at the lack of human fatalities thus far. “If a thirteen-footer can consume a six-foot alligator, it’s only a matter of time,” Kenneth Krysko, at the Florida Museum of Natural History, told me. “Come on! Kids aren’t six feet tall.” A child in a secluded park, or along a canal, would be easiest to snatch. But Snow can imagine other scenarios. More and more pythons are being found around rural homes, he said—“The typical story is ‘Yeah, you know, my chickens have been missing for weeks’ ”—and elsewhere they’ve been known to throttle the occasional pet owner. Pythons seem to have a tremendous homing instinct, he added. Six of the snakes that he has radio-tracked have crawled straight back to the places where they were caught—a journey, in one case, of more than forty-eight miles. “It puts an interesting twist on things,” he said. “If you’re an owner and let a python loose, what are the odds that it will show up at your back door?”

Floridians have some experience with man-eating beasts. Nearly a million and a half native alligators still roam the state—five times as many as thirty years ago, when they were declared endangered—and fatal attacks have tripled in the past decade. (Imagine a million and a half wolves stalking the forests of Wisconsin, a million and a half mountain lions roaming Colorado.) The state’s “nuisance alligator” hot line—1-866-FWC-GATOR—gets more than sixteen thousand calls a year, and tales of close scrapes and pet abductions are a staple of the local news: the cocker spaniel snapped up while cavorting beside a pond, the jogger dragged off a canal embankment, the local pastor yanked underwater while out for a swim. “Most of the time, gators won’t attack,” Allan Woodward, a biologist with Florida Fish and Wildlife, assured me. “It’s just that, every once in a while, they decide to think of humans as prey and give it a try.”

The Burmese python can seem, under the circumstances, like just another local attraction. Americans are schizophrenic when it comes to invasives, Snow says. Every year, we spend well over a hundred billion dollars combatting them—about a quarter of our gross national agricultural product is lost to foreign pests and weeds—and tens of billions importing and selling exotic plants and pets. Florida alone averages one new agricultural pest a month. “We are in a situation now where everything that is imported is largely considered innocent until proven guilty,” Snow said. “But the standard of guilt is too high.” Even if the state can scrape together the money and the know-how for a python-eradication campaign, he said, it may not succeed. A single female python could lay up to a hundred eggs in a clutch, repopulating the state in a matter of years.

Since 1993, a coalition of scientists and environmentalists has urged the federal government to ramp up its efforts against invasives. (“I’ve dragged snake skins through the halls of Congress,” Snow says.) The campaign culminated, last spring, in the proposal of the Nonnative Wildlife Invasion Prevention Act. The act would turn exotic-import laws inside out. Instead of a blacklist of banned species, it would give agents like Eddie McKissick a white list of approved species, screened by the Fish and Wildlife Service. Any animal not on the list couldn’t enter the country. The bill was introduced to Congress by Madeleine Bordallo, a representative from Guam, where brown tree snakes have eaten all but a few of the native songbirds, and was modelled on similar measures in Australia and New Zealand. If it passes, it should reduce exotic imports, simplify inspections, and help prevent future invasions.

But it won’t pass. The pet trade is worth more than forty billion dollars a year in the United States and nearly a hundred million Americans own exotics. (When I mentioned the white list idea to Eddie McKissick, he burst out laughing.) In 1976, the industry blocked a similar measure using the same arguments it uses now. The act would be a “managerial nightmare,” Marshall Meyers, the chief executive officer and general counsel of the Pet Industry Joint Advisory Council, told a House subcommittee last June. More than ten thousand species would have to be screened, many of them barely known to science. If biologists still can’t say whether pythons will stay in Florida or crawl to Brooklyn, how can they predict if any species will become invasive? “Simply on the grounds of Statistics 101, this is unworkable,” Meyers said. “Absent a crystal ball, it is impossible to prove conclusively that no harm has ever nor will ever occur at any time, anywhere in the United States.”

The one statistic that seems to hold true is the rule of ten, described by an English biologist in 1993: one in ten exotics escape into the wild; one in ten of those become established; one in ten established exotics become pests. The rest tend to stay in their cages or cling to their ecological niches. (Or, if we’re very lucky, eat one another: Argentine fire ants, marching north from Alabama, have feasted on Japanese beetles, marching south.) Invasives can undoubtedly drive natives to extinction, as the brown tree snake has shown. But most of the time an ecosystem isn’t a game of musical chairs. When a new species arrives, it rarely takes another’s place. It just finds another spot to sit.

Paul Shafland, the director of Florida Fish and Wildlife’s Non-Native Fish Laboratory, has been tracking local fish populations for more than three decades. Florida’s waterways are home to more than thirty species of exotic freshwater fish, he told me, and their total biomass nearly tripled between 1980 and 2007. Yet the number of native fish hasn’t changed in that period; nor have any natives gone extinct. In 1984, Shafland spearheaded the introduction of the South American butterfly peacock bass to Florida, arguing that it would both control invasive tilapia and make a superb sport fish. Florida anglers now spend nearly ten million dollars a year trying to catch it, giving a substantial boost to the local economy. “Nothing has been displaced,” Shafland said. “We’re just changing the carrying capacity.”

Whether this is a good thing or a bad thing is more of a philosophical question than an ecological one. Shafland, like most fisheries biologists, is used to managing animals for the enjoyment of people. “I’m a consumptive-use conservationist, not a puristic preservationist,” he says. Yet he, too, regrets the changes in Florida. Even a single invasive—the one in a thousand—can transform a landscape, turning a prairie into a forest, a bird sanctuary into a snake pit. And the rest can slowly change the way we see a place. A parrot in Miami is like a McDonald’s in Kathmandu: a sign that you are everywhere and nowhere at once. I asked Shafland the same question I had asked every biologist I’d interviewed: Would you turn back the ecological clock if you could? Like the rest, he didn’t hesitate: “If I had a button on my desk today, and it said that I could eliminate every exotic freshwater fish in Florida, I would push it instantly.”

“We are engaged in a giant experiment that no one can control,” Snow told me, on my last night in the Everglades. “We are throwing these things in with no idea, no thought, no design. The only thing that continues to save us—or, at least, to slow things down—is the rule of ten.” Some exotics may not be able to survive the local winter, but anacondas would be “very comfortable” in the Everglades, Snow believes, and it’s hard not to wonder what other rough beasts are slouching toward Florida. “Let’s not let this happen again,” he said. “I don’t want it to happen again.”

As I was driving back to the airport from the Gulf Coast, two days later, I stopped in a town called Cape Coral, just west of Fort Myers. Carved from more than a hundred square miles of mangroves and piney flatwoods, Cape Coral has grown into a Florida boomtown like any other: it looks as if it were built, badly, last week. Its streets are a labyrinth of subdevelopments and strip malls, interlaced with more than four hundred miles of canals. When it was developed in the late nineteen-fifties, by the Rosen brothers from Baltimore, they promised prospective buyers a “waterfront wonderland.” But the canals haven’t just given people access to the swamp. They’ve given the swamp access to people.

Among the creatures that have lurched into town in recent years is an African lizard called the Nile monitor. Like pythons, monitors were quite popular in the pet trade during the early nineties: Patrick Reynolds remembers seeing hundreds of hatchlings in the reptile warehouse in Homestead. And, like pythons, they are spectacular animals that make terrible pets. Up to seven feet long, with stout legs, tapered jaws, and skin that seems to be encrusted with semiprecious stones, Nile monitors are notoriously aggressive and ill-tempered. When cornered, a monitor will stand on its hind legs and hiss, inflating its body and lashing its tail like a bullwhip. In the words of one biologist, “No one realizes the ability this animal has to tear off your cat’s head with one twist.” In the wild, monitors hunt on land or in the water, climbing trees, digging up burrows, or simply chasing down their prey: an adult monitor can outrun a human, though it will usually attack only when cornered. One wildlife bulletin from the U.S. Geological Survey called the species “omnicarnivorous.”

Cape Coral is forty miles from Big Cypress Swamp as the crow flies, and another twenty from the Everglades—a habitat very similar to the Upper Nile. The monitors could wreak havoc on the park’s bird and turtle populations, but they seem in no great hurry to get there. The hunting is just fine where they are. Their population is now in the thousands, Todd Campbell, a biologist at the University of Tampa, told me, and growing alarmingly. Campbell has been trapping and radio-tracking the lizards for six years, with the city’s help. “They’re very aware, very intelligent,” he said. “You look in their eyes and—I’m not being weird here—it’s more like you’re looking at a bird or a mammal than some dumb pea-brained snake.” Monitors often hunt in packs, like modern-day velociraptors, smelling for prey with their extremely sensitive tongues. When Campbell dissects them, he finds whole clutches of turtle or bird eggs in their bellies, and large boluses of fur, often from local pets. “They will eat anything that will fit in their mouths,” he said. “And if they can’t fit it in they’ll tear it limb from limb.”

Before I left town, I visited a local schoolteacher named Robin Snyder, who’d had some run-ins with the lizards. Her house was on a cul-de-sac beside a canal, with vacant lots on either side where the lizards breed. “They’re getting braver and braver,” she told me. “We went on vacation last summer, and when we got back a monitor had taken over our porch. It would sit on our front patio like it was a dog.” The lizards had eaten her neighbor’s poodle, she added, and they liked to snack on the town’s rare burrowing owls. “It’s like they’re having a little shrimp cocktail or something.” Two years ago, Snyder was pruning a bush when a monitor took a chunk out of her hand. Another bit her Border collie on the face, nearly taking out its eye. “That dog isn’t afraid of anything,” she said. “But now I have to drag her outside. She smells their urine.”

Snyder is an earthy brunette, fifty years old, with long, untamed hair. She grew up in the hills of Virginia and is used to having bears and bobcats around. But these things are different, she said. “They’ll just come right on out in the middle of the day.” The city’s nuisance hunter had already trapped ten or twelve in the “lizard condominium” next to her house. And a local woman, nicknamed Annie Oakley, had shot fourteen from her window with a pellet gun. But there always seemed to be more. “People are actually eatin’ ’em over at Pine Island,” Snyder said. “A guy I went to school with said they’re pretty good.” She smirked. Her son was grown and her husband had taken a job back in Virginia, she said. “So now it’s just me and the dog and the lizards.” Behind her, in the deepening dusk, the waters of the canal had darkened from green to gray and the murmur of the swamp had begun to rise. “I’m homesick for the mountains,” she said. ♦

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